1. Technical Field
The present invention relates to a system, and process for use thereof, for inspecting wafers and other semiconductor or microelectronic substrates.
2. Background Information
Over the past several decades, microelectronics and semiconductors have exponentially grown in use and popularity. Microelectronics and semiconductors have in effect revolutionized society by introducing computers, electronic advances, and generally revolutionizing many previously difficult, expensive and/or time consuming mechanical processes into simplistic and quick electronic processes. This boom has been fueled by an insatiable desire by business and individuals for computers and electronics, and more particularly, faster, more advanced computers and electronics whether it be on an assembly line, on test equipment in a lab, on the personal computer at one's desk, or in the home via electronics and toys.
The manufacturers of microelectronics and semiconductors have made vast improvements in end product quality, speed and performance as well as in manufacturing process quality, speed and performance. However, there continues to be demand for faster, more reliable and higher performing semiconductors.
One process that has evolved over the past decade plus is the microelectronic and semiconductor inspection process. The merit in inspecting microelectronics and semiconductors throughout the manufacturing process is obvious in that bad wafers may be removed at the various steps rather than processed to completion only to find out a defect exists either by end inspection or by failure during use. In the beginning, wafers and like substrates were manually inspected, such as by humans using microscopes. As the process has evolved, many different systems, devices, apparatus, and methods have been developed to automate this process, such as the method developed by August Technology and disclosed in U.S. Pat. No. 6,324,298, which is incorporated herein by reference. Many of these automated inspection systems, devices, apparatus, and methods focus on two dimensional inspection, that is inspection of wafers or substrates that are substantially or mostly planar in nature.
One of the most important parameters that need to be controlled for any optical wafer inspection system such as that described above is keeping the focus of the inspection device, such as an optical sensor or camera, within the depth of field of the lens used. Typically this is done in one to two ways: 1) adding a focus sensor into the optical path and measuring the quality of the focus at all times whereby the feedback from this sensor is sent to a motion controller, which in turn adjusts the focus mechanism to keep the system in focus, or 2) moving the camera through a range of heights and taking pictures of the wafer at each height, and then using an image processing algorithm to determine the height of best focus. Each of these techniques has it own set of problems. One problem with the first technique is that at higher inspection stage velocities (>100 mm/sec), these types of sensors do not have the capability to guarantee that the image stays in focus because of rapid motion of the inspection stage during the inspection process. The problems with the second technique include time and video focus. As to time, it just takes too long to use video focus on an array of points as it typically takes 1–2 seconds per focus point. As to video focus, in many steps during wafer processing there is very little pattern on the wafer, which makes a video focusing algorithm impossible to implement because the system cannot get any information to use to determine the best focus height.